The basal titanosaurian Rukwatitan bisepultus (Dinosauria, Sauropoda) from the middle Cretaceous Galula Formation, Rukwa Rift Basin, southwestern Tanzania

ABSTRACT

Whereas titanosaurians represent the most diverse and cosmopolitan clade of Cretaceous sauropod dinosaurs, they remain rare components of Cretaceous African faunas. Currently recognized continental African titanosaurians include Aegyptosaurus baharijensis and Paralititan stromeri from early Upper Cretaceous deposits near Bahariya Oasis, Egypt, and Malawisaurus dixeyi and Karongasaurus gittelmani from the Lower Cretaceous (∼Aptian) Dinosaur Beds of Malawi, in addition to several undesignated and fragmentary forms across the continent. Here, we describe a new titanosaurian taxon, Rukwatitan bisepultus, on the basis of a partial, semiarticulated postcranial skeleton recovered from the middle Cretaceous Galula Formation in southwestern Tanzania. Unique to Rukwatitan are carotid processes on posterior cervical vertebrae, a deep coracobrachialis fossa and subquadrangular cross-section of the humerus, and a slender, curved, teardrop-shaped pubic peduncle on the ilium. Parsimony and Bayesian phylogenetic analyses of 35 sauropod taxa congruently place Rukwatitan as a non-lithostrotian titanosaurian, a relationship supported by cervical vertebrae with undivided pleurocoels and strongly procoelous anterior caudal vertebrae. Rukwatitan differs from the potentially penecontemporaneous and geographically proximate Malawisaurus by exhibiting weakly developed chevron articulations and posteriorly inclined neural spines on the middle caudal vertebrae, a proximally robust and distally unexpanded humerus, and an anteroventrally elongated coracoid. Similar to biogeographic patterns identified in certain crocodyliform clades (e.g., small-bodied notosuchians), titanosaurians on continental Africa appear to exhibit a regional (e.g., southern versus northern Africa), rather than a continental- or supercontinental-level signal.

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ACKNOWLEDGMENTS

We thank D. Kamamba, F. Ndunguru, J. Temba, and J. Temu (Tanzania Antiquities Unit), P. Msemwa (formerly of Tanzania Museum of House of Culture), S. Ngasala, I. Marobhe, and N. Boniface (University of Dar es Salaam), and the Tanzania Commission for Science and Technology (COSTECH) for logistical and administrative support; E. K. Lund, S. Egberts, K. Melstrom, and W. Holloway for assistance with mechanical and digital preparation; members of the 2007 and 2008 Rukwa Rift Basin Project expeditions for field assistance; H. and M. Faessler for continued support in Mbeya; E. Gomani for specimen access in the collections at the Malawi Division of Antiquities; M. D’Emic and M. Carrano for fruitful discussions; J. Sattler (Ohio University Heritage College of Osteopathic Medicine) for photography; and B. Keaner, C. Pugh, and J. Sands (Holzer Clinic, Athens, Ohio) for assistance with computed tomography scanning. M. D’Emic and P. Mannion provided extremely useful reviews of the original submission of this contribution. This research was supported by the U.S. National Science Foundation (NSF EAR 0617561, EAR 0854218, EAR 0933619), the National Geographic Society (CRE), and the Ohio University Heritage College of Osteopathic Medicine and Ohio University Office of Research and Sponsored Programs.

Handling editor: Hailu You.